Facile large scale solution synthesis of nanostructured iron, nickel and cobalt telluride and possible applications

Hong, Sungbum
Major Professor
Yue Wu
Committee Member
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Chemical and Biological Engineering

Transition metal chalcogenides existing in a wide variety of stoichiometries have shown captivating electrical performances. Among them, the earth-abundance and environmental friendliness of iron (Fe), cobalt (Co) and nickel (Ni) chalcogenides have dragged scientists’ attention. Moreover, as state-of-art nanotechnology has impacted on conventional bulk technology in regard to enhancement in performance and discovery of new characteristics, it has been found that nanostructured the Fe, Co and Ni chalcogenides can be exploited for many applications such as superconductor, battery, thermoelectric materials and magnetic material, yet synthesis of these materials has been only accomplished in several milligram scales and normally involved costly equipment and extreme reaction conditions.

This thesis proposes facile one-pot solution synthesis methods of nanostructured FeTe2, CoTe and NiTe with over 80% yielding and ~7.0g of final product per batch. An ethylene glycol based system enables a mild reaction condition and short reaction time. The as-synthesized FeTe2 show 1-D nanowires with 26 à  à ± 6nm diameters and a usage of hydrazine for the reaction is appeared to be a key factor to acquire uniform morphology. CoTe and NiTe are synthesized by a one-step reaction. The CoTe 1-D nanorods with uniform thickness of 11 à  à ± 2nm are synthesized only by 5 minutes of reaction and the NiTe 2-D nanoparticles and its conjugated structures with 12 à  à ± 3nm diameters are obtained by 4 hours of reaction. The final solution is further washed, dried and pulverized.

The materials powder is spark plasma sintered (SPSed) into disks, and then seebeck coefficient and electrical conductivity are measured. For FeTe2, although it behaves as an intrinsic semiconductor materials, an unusual p-n conduction switching behavior of FeTe2 is observed, which is possibly because of the unintentional tellurium n-type doping generated by thermally expanded cell can attribute to the behavior. As an application of this behavior, a preliminary experiment of thermally controllable p-n junction diode is managed to show a partial success. Meanwhile, the substantially lower seebeck coefficient and higher electrical conductivity in of NiTe and CoTe agree with the highly metallic behaviors, leaving a possible application as dopants for other semiconductor application.